1. Field
The following description relates to passive optical network (PON) technology, and more particularly, to optical layer monitoring technology in a PON.
2. Description of the Related Art
Along with an increase in demand for broadband services such as VOD, CATV, or HDTV, a passive optical network (PON) for supplying high speed and large volume data services to subscribers has been actively constructed. As representative PON technology, time division multiplexing PON technology in which subscribers of several communication services share and use downstream signals and upstream signals which have the same wavelength, and transmit the upstream signals to a telephone company of network service providers only in a use band allocated over time, may be given. As a representative example of time division multiplexing PON technology, Ethernet PON (EPON), Giga-capable PON (GPON), or the like, may be given. Also, as representative PON technology, wavelength division multiplexing PON (WDM-PON) technology in which a plurality of subscribers use downstream signals and upstream signals which have different wavelengths, may be given.
In such a PON, an optical transmission apparatus used in the telephone company side of a network service provider, and an optical transmission apparatus used in the communication service subscriber side are connected with each other using an optical fiber as a transmission medium of signals. Accordingly, in order to reliably operate a PON, the network service provider should continuously monitor the operational status of an optical path so as to detect distortion or attenuation, and to quickly recover from the distortion or attenuation along the optical path when distortion or attenuation is detected. In addition, during the optical path monitoring and distortion or attenuation recovery process, it is preferable that services provided to the subscribers are not broken or disrupted.
As an optical layer monitoring apparatus for solving these problems, an optical time-domain reflectometer (OTDR) is widely used. OTDR is an apparatus that makes an OTDR signal including optical pulses, incident on an optical path to be monitored, receives a backward scattering signal generated along the optical path due to the OTDR signal, and then analyzes the received signal over time to thereby measure a loss in accordance with a length of the optical path, a position of a connection point, a connection loss, and the like.